Method for controlling ECM motor to output constant torque

ABSTRACT

A method for controlling an ECM motor to output a constant torque. The method includes: 1) entering a target torque value T0 from an external device; when the motor is in a non-use state, starting the motor, and allowing the microprocessor to acquire an original output voltage value P chopped by a PWM signal; when the motor is in a running state, allowing the microprocessor to acquire a current output voltage value P chopped by the PWM signal; 2) enabling the microprocessor to calculate a target bus current value Itad using the function Itad=F(T,P) according to the target torque value T0 and the output voltage value P chopped by the PWM signal; and detecting a real-time bus current Ibus; and 3) allowing the microprocessor to compare the target bus current value Itad with the real-time bus current Ibus for conducting a closed-loop control.

CROSS-REFERENCE TO RELATED APPLICATIONS

Pursuant to 35 U.S.C. §119 and the Paris Convention Treaty, thisapplication claims the benefit of Chinese Patent Application No.201310518422.3 filed Oct. 28, 2013, the contents of which areincorporated herein by reference. Inquiries from the public toapplicants or assignees concerning this document or the relatedapplications should be directed to: Matthias Scholl P.C., Attn.: Dr.Matthias Scholl Esq., 245 First Street, 18th Floor, Cambridge, Mass.02142.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for controlling an ECM motor to outputa constant torque.

2. Description of the Related Art

Electronically commutated motors (ECM) or DC brushless permanent magnetsynchronous motors generally have three control modes including aconstant rotational speed control mode, a constant torque control mode,and a constant air volume control mode, of which, the constant torquecontrol mode is commonly used. A currently used vector control mode hascomplicate mathematical model, troublesome operation, high demands onthe arithmetic capability of a central processing unit (CPU), therebyresulting in high production costs. A typical constant torque controlmode is conducted by scale control of the bus current; however, such acontrol mode is complicated and has a plurality of variables therebyresulting in poor control accuracy.

SUMMARY OF THE INVENTION

In view of the above-described problems, it is one objective of theinvention to provide a method for controlling an ECM motor to output aconstant torque. The method has simple mathematic model and algorithm,low operational requirements on the CPU, low production costs, and highcontrol accuracy.

To achieve the above objective, in accordance with one embodiment of theinvention, there is provided a method for controlling an ECM motor tooutput a constant torque. The ECM motor comprises: a stator assembly, arotor assembly, a housing assembly, and a motor controller. The motorcontroller comprises a power supply circuit, a microprocessor, aninverter, and a rotor position detection circuit. The power supplycircuit supplies power to each circuit. The rotor position detectioncircuit detects a rotor position signal and inputting the rotor positionsignal into the microprocessor. The microprocessor controls the invertercircuit. The inverter circuit controls each coil winding of the statorassembly to be in a power-off state or a power-on state. The methodcomprises the following steps:

1) entering a target torque value T0 from an external device; when themotor is in a non-use state, starting the motor, and allowing themicroprocessor to acquire an original output voltage value P chopped bya PWM signal; when the motor is in a running state, allowing themicroprocessor to acquire a current output voltage value chopped by thePWM signal;

2) enabling the microprocessor to calculate a target bus current valueItad using the function Itad=F(T,P) according to the target torque valueT0 and the output voltage value P chopped by the PWM signal, in which,Itad represents a target bus current, T represents a torque value outputby the motor, P represents the output voltage value chopped by the PWMsignal input to the inverter circuit by the microprocessor; anddetecting a real-time bus current Ibus; and

3) allowing the microprocessor to compare the target bus current valueItad with the real-time bus current Ibus for conducting a closed-loopcontrol: when the target bus current Itad is larger than the real-timebus current Ibus, increasing the output voltage value P chopped by thePWM signal; when the target bus current Itad is smaller than thereal-time bus current Ibus, decreasing the output voltage value Pchopped by the PWM signal; and when the target bus current Itad is equalto the real-time bus current Ibus, stopping regulating the outputvoltage value P chopped by the PWM signal, and allowing the ECM motor toenter a running state, and repeating step 2) for conducting a constantcontrol state.

In a class of this embodiment, that the target bus current Itad is equalto the real-time bus current Ibus means that an error of a deviation ofthe real-time bus current Ibus from the target bus current Itad iswithin 1%.

In a class of this embodiment, the function Itad=F(T,P) in step 2) isItad=K1+K2*T+K3*P+K4*T*P, in which, K1, K2, K3, and K4 representcoefficients, T represent the torque, and P represents the outputvoltage value chopped by the PWM signal.

In a class of this embodiment, the function Itad=F(T,P) relating to thetorque value output by the motor and a DC bus current is established byexperimental means.

Advantages according to embodiments of the invention are summarized asfollows:

Experimental means are utilized to obtain the function Itad=F(T,P)relating to the torque value output by the motor and a DC bus current,and the microprocessor calculates the target bus current value Itad byusing the function Itad=F(T,P) according to the target torque value T0.The microprocessor compares the target bus current value Itad with thereal-time bus current Ibus for conducting a closed-loop control: whenthe target bus current Itad is larger than the real-time bus currentIbus, increase a duty cycle P of the PWM signal input into the inverterfrom the microprocessor; when the target bus current Itad is smallerthan the real-time bus current Ibus, decrease the duty cycle P of thePWM signal input into the inverter from the microprocessor; and when thetarget bus current Itad is equal to the real-time bus current Ibus, stopregulating the duty cycle P of the PWM signal input into the inverterfrom the microprocessor. Thus, the number of control variables isdecreased, the mathematical model is simple, and microprocessors of CPUor MCU having low arithmetic capability are applicable, thereby largelydecreasing production costs. Meanwhile, by using the closed-loop controland the full measurements of the experimental means, the accuracy of thecontrol is effectively ensured.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described hereinbelow with reference to theaccompanying drawings, in which:

FIG. 1 is a stereogram of an ECM motor in accordance with one embodimentof the invention;

FIG. 2 is a stereogram of a motor controller of an ECM motor inaccordance with one embodiment of the invention;

FIG. 3 is a sectional view of an ECM motor in accordance with oneembodiment of the invention;

FIG. 4 is a circuit block diagram of a motor controller of an ECM motor;

FIG. 5 is a circuit diagram of FIG. 4;

FIG. 6 is a control flow graph of a method for controlling an ECM motorto output a constant torque in accordance with one embodiment of theinvention; and

FIG. 7 is a connection diagram of an ECM motor and a dynamometer inaccordance with one embodiment of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

For further illustrating the invention, experiments detailing a methodfor controlling an ECM motor to output a constant torque are describedbelow. It should be noted that the following examples are intended todescribe and not to limit the invention.

As shown in FIGS. 1-3, an ECM motor generally comprises a motorcontroller 2 and a motor body 1. The motor body 1 comprises a statorassembly 12, a rotor assembly 13, and a housing assembly 11. The statorassembly 13 is mounted on the housing assembly 11. The motor body 1 isprovided with a hall sensor 14 for detecting a rotor position. The rotorassembly 13 is nested within or outside the stator assembly 12. Themotor controller 2 comprises a control box 22 and a control board 21disposed in the control box 22. The control board 21 generallycomprises: a power supply circuit, a microprocessor, a bus currentdetection circuit, an inverter circuit, and a rotor position detectioncircuit 14 (the hall sensor). The power supply circuit supplies power toeach circuit. The rotor position detection circuit detects a signal ofthe rotor position and sends the signal of the rotor position to themicroprocessor. The bus current detection circuit detects a bus currentto the microprocessor, the microprocessor controls the inverter circuit,and the inverter circuit further controls a power-off or power-on stateof each coil winding of the stator assembly 12.

As shown in FIGS. 4-5, assuming that the ECM motor is a three-phasebrushless DC permanent magnet synchronous motor, the rotor positiondetection circuit 14 generally comprises three hall sensors thatrespectively detect a rotor position in a 360° of electric angle cycle,the energization state of each coil winding of the stator assembly 12changes when the rotator rotates for every 120° of the electric anglecycle, thereby forming a three-phase six-step control mode. The AC inputpasses through a full-wave rectifying circuit formed by diodes D7, D8,D9, and D10, and outputs a DC bus voltage Vbus at one end of acapacitance C1. The DC bus voltage Vbus is related to the voltage of theAC input, and once the voltage of the AC input is determined, the busvoltage Vbus is constant. A line voltage P of the three-phase winding isan output voltage of a PWM chopper, P=Vbus*w, in which, w represents aduty cycle of a PWM signal input into the inverter circuit from themicroprocessor, and the DC bus current Ibus varies along with the changeof the line voltage P. The inverter circuit comprises electric switchingtubes Q1, Q2, Q3, Q4, Q5, and Q6. Control ends of the electric switchingtubes Q1, Q2, Q3, Q4, Q5, and Q6 are respectively controlled by sixlines of PWM signals (P1, P2, P3, P4, P5, and P6) output by themicroprocessor. The inverter circuit is also connected to a resistanceR1 for detecting the bus current Ibus, and a circuit for detecting thebus current converts the bus current Ibus detected by the resistance R1and transmits the converted bus current Ibus to the microprocessor.

As shown in FIG. 6-7, a method for controlling an ECM motor to output aconstant torque is provided. The ECM motor comprises: the statorassembly, the rotor assembly, the housing assembly, and the motorcontroller. The motor controller comprises the power supply circuit, themicroprocessor, the inverter, and the rotor position detection circuit.The power supply circuit supplies power to each circuit. The rotorposition detection circuit detects the rotor position signal andinputting the rotor position signal into the microprocessor. Themicroprocessor controls the inverter circuit. The inverter circuitcontrols each coil winding of the stator assembly to be in the power-offstate or the power-on state. The method comprises the following steps:

1) entering a target torque value T0 from an external device; when themotor is in a non-use state, starting the motor, and allowing themicroprocessor to acquire an original output voltage value P chopped bya PWM signal; when the motor is in a running state, allowing themicroprocessor to acquire a current output voltage value chopped by thePWM signal;

2) enabling the microprocessor to calculate a target bus current valueItad using the function Itad=F(T,P) according to the target torque valueT0 and the output voltage value P chopped by the PWM signal, in which,Itad represents a target bus current, T represents a torque value outputby the motor, P represents the output voltage value chopped by the PWMsignal input to the inverter circuit by the microprocessor; anddetecting a real-time bus current Ibus; and

3) allowing the microprocessor to compare the target bus current valueItad with the real-time bus current Ibus for conducting a closed-loopcontrol: when the target bus current Itad is larger than the real-timebus current Ibus, increasing the output voltage value P chopped by thePWM signal; when the target bus current Itad is smaller than thereal-time bus current Ibus, decreasing the output voltage value Pchopped by the PWM signal; and when the target bus current Itad is equalto the real-time bus current Ibus, stopping regulating the outputvoltage value P chopped by the PWM signal, and allowing the ECM motor toenter a running state, and repeating step 2) for conducting a constantcontrol state.

When the target bus current Itad is equal to the real-time bus currentIbus, it refers that an error of a deviation of the real-time buscurrent Ibus from the target bus current Itad is within 1%.

The function Itad=F(T,P) in step 2) is Itad=K1+K2*T+K3*P+K4*T*P, inwhich, K1, K2, K3, and K4 represent coefficients, T represent thetorque, and P represents the output voltage value chopped by the PWMsignal.

The function Itad=F(T,P) relating to the torque value output by themotor and a DC bus current is established by experimental means.

As shown in FIG. 7, a certain type of ECM motor is selected, and in anopen-loop mode, a dynamometer is used to test the DC bus currents of theECM motor in conditions of different output voltages chopped by the PWMsignal and different torques, as shown in Table 1.

TABLE 1 DC bus current Itad in conditions of different output voltageschopped by the PWM signal and different torques Output voltage value Pchopped by a PWM Output torque Detected DC bus Testing signal in an openloop T loaded by a current Itad output point mode of a controllerdynamometer by a controller 1 95%*Vbus 0.5 Nm 25 2 90%*Vbus 3.0 Nm 38 385%*Vbus 1.5 Nm 52 4 80%*Vbus 5.0 Nm 65 5 75%*Vbus 2.5 Nm 78 6 70%*Vbus3.0 Nm 88 7 65%*Vbus 4.0 Nm 96 8 60%*Vbus 0.5 Nm 117 9 55%*Vbus 1.0 Nm130 10 50%*Vbus 6.0 Nm 144 11 45%*Vbus 2.0 Nm 158 12 40%*Vbus 2.5 Nm 17113 88%*Vbus 3.0 Nm 185 14 78%*Vbus 5.0 Nm 200 15 68%*Vbus 4.5 Nm 35 1635%*Vbus 0.5 Nm 50 17 30%*Vbus 1.0 Nm 74 18 50%*Vbus 7.0 Nm 89 1925%*Vbus 2.0 Nm 104 20 20%*Vbus 4.0 Nm 119 21 15%*Vbus 3.0 Nm 136

Because the DC bus current is only related to the output voltage Pchopped by the PWM signal and the output torque T of the motor, atwo-variable linear equation Itad=K1+K2*T+K3*P+K4*T*P is established.Four testing points are optionally selected from Table 1, the DC buscurrent Itad, the output torque T loaded by the dynamometer, and theoutput voltage value P chopped by the PWM signal are respectively placedin the function Itad=K1+K2*T+K3*P+K4*T*P to obtain four sets ofequations, and a set of coefficients K1, K2, K3, and K4 are calculated.Another four different testing points are selected, the DC bus currentItad, the output torque T loaded by the dynamometer, and the outputvoltage value P chopped by the PWM signal are respectively placed in thefunction Itad=K1+K2*T+K3*P+K4*T*P to obtain another four sets ofequations, and another set of coefficients K1, K2, K3, and K4 arecalculated. Thus, a plurality of sets of coefficients K1, K2, K3, and K4are calculated, and the function Itad=F(T,P) is obtained byoptimization.

The constant torque control is conducted by the microprocessor byprogramming. The target torque T0 is input from the external device.When the motor is in the non-use state, the motor is started, and themicroprocessor acquires the original voltage value P chopped by the PWMsignal. When the motor is in the running state, the microprocessoracquires the current output voltage value P chopped by the PWM signal.The microprocessor calculates the target bus current value Itad usingthe function Itad=F(T,P) according to the target torque value T0 and theoutput voltage value P chopped by the PWM signal, and the real-time buscurrent Ibus is detected. The microprocessor compares the target buscurrent value Itad and the real-time bus current value Ibus according tothe real-time bus current Ibus to correspondingly regulate the outputvoltage value P chopped by the PWM signal for conducting the closed-loopcontrol.

In the open loop mode, DC bus current values of the ECM motor are testedby the dynamometer in conditions of different duty cycles P of the PWMsignal and different torque values to form N sets of testing data. Themore data are tested, which means the more testing points are, thehigher accuracy of the function Itad=F(T,P) is, and the number and therange of the testing points are selected according to the controlaccuracy.

While particular embodiments of the invention have been shown anddescribed, it will be obvious to those skilled in the art that changesand modifications may be made without departing from the invention inits broader aspects, and therefore, the aim in the appended claims is tocover all such changes and modifications as fall within the true spiritand scope of the invention.

The invention claimed is:
 1. A method for controlling an ECM motor tooutput a constant torque, the ECM motor comprising: a stator assembly, arotor assembly, a housing assembly, and a motor controller; the motorcontroller comprising: a power supply circuit, a microprocessor, aninverter, and a rotor position detection circuit; the power supplycircuit supplying power to each circuit; the rotor position detectioncircuit detecting a rotor position signal and inputting the rotorposition signal into the microprocessor; the microprocessor controllingthe inverter circuit; and the inverter circuit controlling each coilwinding of the stator assembly to be in a power-off state or a power-onstate; the method comprising the following steps: 1) entering a targettorque value T0 from an external device; when the motor is in a non-usestate, starting the motor, and allowing the microprocessor to acquire anoriginal output voltage value P chopped by a PWM signal; when the motoris in a running state, allowing the microprocessor to acquire a currentoutput voltage value P chopped by the PWM signal; 2) enabling themicroprocessor to calculate a target bus current value Itad using thefunction Itad=F(T,P) according to the target torque value T0 and theoutput voltage value P chopped by the PWM signal, in which, Itadrepresents a target bus current, T represents a torque value output bythe motor, P represents the output voltage value chopped by the PWMsignal input to the inverter circuit by the microprocessor; anddetecting a real-time bus current Ibus; and 3) allowing themicroprocessor to compare the target bus current value Itad with thereal-time bus current Ibus for conducting a closed-loop control: whenthe target bus current Itad is larger than the real-time bus currentIbus, increasing the output voltage value P chopped by the PWM signal;when the target bus current Itad is smaller than the real-time buscurrent Ibus, decreasing the output voltage value P chopped by the PWMsignal; and when the target bus current Itad is equal to the real-timebus current Ibus, stopping regulating the output voltage value P choppedby the PWM signal, and allowing the ECM motor to enter a running state,and repeating step 2) for conducting a constant control state.
 2. Themethod of claim 1, wherein that the target bus current Itad is equal tothe real-time bus current Ibus means that an error of a deviation of thereal-time bus current Ibus from the target bus current Itad is within1%.
 3. The method of claim 2, wherein the function Itad=F(T,P) in step2) is Itad=K1+K2*T+K3*P+K4*T*P, in which, K1, K2, K3, and K4 representcoefficients, T represent the torque, and P represents the outputvoltage value chopped by the PWM signal.
 4. The method of claim 2,wherein the function Itad=F(T,P) relating to the torque value output bythe motor and a DC bus current is established by experimental means.